This invention relates to an apparatus for adjusting the sieve of a combine harvester which can be provided either as a device attached to an existing combine harvester or can be provided as a kit of parts for attachment to a combine harvester to provide the necessary adjustment.
As is well known, a combine harvester generally comprises a frame mounted on ground wheels for movement across the ground in a working direction, a cab in which the operator will sit for steering and controlling the combine, a header for picking up the crop to be harvested either in the form of a swath or directly cutting a standing crop, a straw separation arrangement generally in the form of a cylinder and straw walkers which separate grain and chaff from the straw of the crop, and a sieve onto which the separated grain and chaff are deposited for separation of the grain from the chaff generally using an air flow through the sieve which acts differentially upon the grain and the chaff.
The combine often includes a control arrangement mounted within the cab for varying the speed of the fan motor so as to increase and decrease the air flow through the sieve. It will be appreciated that the air flow conditions are particularly important in ensuring proper separation of the grain and the chaff and those conditions will vary significantly depending upon various parameters. In some cases those parameters are relatively coarse for example the type of crop to be harvested. In other cases the parameters are very fine and significant variations can be noted from such matters as the ripeness of the crop which can vary across a field to be harvested and the humidity of the climatic conditions which can of course vary during the day.
The speed of the fan is a relatively coarse adjustment which must be made to provide the necessary coarse adjustments mentioned above. In addition the condition of the sieve can also be adjusted, that is the angle of the openings through the sieve, since the air flow conditions are dependent not only upon the amount of air flow and its velocity but also the angle and size of the openings in the sieve.
Most combines provide a lever mechanism which mechanically operates the openings or louvers in the sieve so that the openings can be adjusted. The mechanical lever arrangement is however positioned at the sieve and generally can only be actuated by an operative climbing from the cab, halting operation of the combine, moving to the rear of the combine and actuating the levers to a position which can be measured by experienced eye or in some cases by a measuring gauge.
There is a great reluctance therefore for the operative or user to carry out such adjustments particularly during the operating time and hence the fine adjustment which is possible by the adjustment of the sieve is generally not made. The operative therefore sets the sieve initially at a compromise position which achieves an acceptable level of grain separation while avoiding an unacceptable amount of grain loss over the rear end of the sieve.